This invention relates to an RF (radio frequency) circuit module and, more particularly, to an RF circuit module for use mainly in VHF band, UHF band, microwave band and mm-wave band.
FIG. 11 illustrates an example of a conventional RF circuit module disclosed in Japanese Patent Laid-Open No. 8-148800. In FIG. 11, the reference numeral 31 is a multi-layered first dielectric circuit board, 32 is a multi-layered second dielectric circuit board, 33 are via holes which are connecting members, 34 is a high frequency circuit element which is a first RF semiconductor device, 35 is a surface mounting component which is a second RF semiconductor device, 36 is a DC line, 37 is a ground pattern which is a ground conductor, 38 is a connection portion disposed on the first dielectric circuit board 31 in order to establish the connection between a DC line 31a of the first dielectric circuit board 31 and a DC line 32a of the second dielectric circuit board 32, and 39 is a cavity. The high frequency circuit element 34 is mounted within the cavity 39, and the second dielectric circuit board 32 is mounted on the top surface around the cavity 39, and the ground pattern 37 on the rear surface of the second dielectric circuit board 32 and the via holes 33 around the cavity 39. Also, the surface mounting component 35 is mounted on the second dielectric circuit board 32. The DC line 31a of the first dielectric circuit board 31 and the DC line 32a of the second dielectric circuit board 32 are connected to each other by overlapping of the respective DC lines 31a and 32a. 
In the illustrated RF circuit module structure, the ground pattern 37 on the bottom surface of the second dielectric circuit board 32 is connected to the via holes 33 around the cavity 39, so that the cavity 39 is electrically shielded and hermetically sealed. Also, the surface mounting component 35 can be mounted onto the second dielectric circuit board 32, allowing the circuit to have a high mounting density.
However, since the conventional RF circuit module has the above-described structure, while the high frequency circuit element 34 mounted within the cavity 39 can be hermetically sealed, the circuit on the second dielectric circuit board 32 cannot be hermetically sealed. For this reason, there is a drawback which is that the surface mounting component 35 mounted on the second dielectric circuit board 32 must be separately sealed.
Also, since the provision of the connecting portion 38 is necessary to connect together the DC line 31a of the first dielectric circuit board 31 and the DC line 32a of the second dielectric circuit board 32, there is a drawback which is that both the resulting circuit size and the manufacturing cost are increased.
Accordingly, the present invention is aimed at solving the above described drawbacks of the conventional design. An object of the present invention is to provide an RF circuit module in which the high frequency circuit elements which are RF semiconductor devices mounted on the first dielectric circuit board and the second dielectric circuit board can easily be electrically shielded and hermetically sealed. Another object of the present invention is to reduce the size and improve the performance of the RF circuit module.
With the above object in view, the RF circuit module of the present invention comprises a multi-layered first dielectric circuit board in which a cavity surrounded by a wall is formed in an upper layer, a first RF semiconductor device mounted within the cavity on the first dielectric circuit board, a second dielectric circuit board of at least one layer connected at an upper surface of the wall to the first dielectric circuit board and having a ground conductor disposed on its bottom surface, a second RF semiconductor device mounted to the upper surface of the second dielectric circuit board. A metal cover is provided to cover the second dielectric circuit board and the second RF semiconductor device. The metal cover is connected at the upper surface of the wall to the first dielectric circuit board, thus providing an electric shield for the second RF semiconductor device and a hermetic seal for the first and second RF semiconductor device.
The first dielectric circuit board may comprise a dielectric member surrounding the second dielectric circuit board and the metal cover may have a plate-like shape.
According to the present invention, the RF circuit module comprises a first dielectric circuit board having defined in a first surface a cavity surrounded by a wall, a first RF semiconductor device mounted within the cavity of the first dielectric circuit board, a second dielectric circuit board placed on the wall of the first dielectric circuit board, and a second RF semiconductor device mounted to the second dielectric circuit board. A metal base is disposed on a second surface of the first dielectric circuit board and a number of embedded conductors are embedded within the wall and arranged to surround the cavity so that each has one end electrically connected to the metal base and the other end exposed from the first surface and arranged to surround the cavity. A metal cover is sealingly attached to the first dielectric circuit board to cover the second dielectric circuit board and the second RF semiconductor device. The metal cover is electrically connected at the upper surface of the wall, whereby the first and second RF semiconductor devices are electrically shielded and hermetically sealed.
The wall may comprise an extension portion having defined therein a second cavity for surrounding the second dielectric circuit board and the second RF semiconductor device, and the metal cover may have a plate-like shape.
The first dielectric circuit board may be a high-temperature burned circuit board while the second dielectric circuit board may be a low-temperature burned circuit board.
The first dielectric circuit board and the second dielectric circuit board may be electrically connected to each other either through a solder bump or an anisotropic conductive sheet.
The RF circuit module may further comprise a high-frequency circuit device, which is not necessary to be hermetically sealed, mounted on the first dielectric circuit board outside of the metal cover.
The first dielectric circuit board may includes a stepped portion for mounting the high-frequency circuit device thereon.
The metal base on the first dielectric circuit board may be exposed to the bottom of the cavity.
The first dielectric circuit board may have mounted thereon a transmission circuit and the second dielectric circuit board may have mounted thereon a reception circuit.